For two years, a deadly strain of chicken flu known as H5N1 has been killing birds in Asia. While slightly more than 100 people are known to have contracted the disease, and 60 of them have died, there is still no sign that the flu has begun to spread from person to person.

That hasn't prevented a recent outbreak of apocalyptic warnings from health officials and experts about the specter of a worldwide pandemic. In Hurricane Katrina's wake, health officials in the United States are talking more and more about pandemic preparation. Some of these ideas -- such as stockpiling vaccines -- are sensible, whether or not bird flu turns into a human disease and begins to spread rapidly.

But other ideas aren't. A few scientists have suggested "priming" people with a dose of the new vaccine against H5N1 before we even know whether a pandemic is coming. Vaccinating large numbers of people against a disease that may never appear carries its own risks. Remember the swine flu debacle of 1976? At least 25 people died from vaccine complications and no epidemic ever erupted. That should be warning enough.

Another dangerous idea for pandemic preparation has come from President Bush. Earlier this month, he suggested using the military to enforce a quarantine. "Who [is] best to be able to effect a quarantine?" he asked rhetorically at a press conference. "One option is the use of a military that's able to plan and move."

The very term quarantine can be misunderstood (not to mention the military's role). Did the president mean gathering those exposed to flu in a single location and forcing them to stay there? Did he mean isolating them in their homes? Cordoning off whole communities where cases crop up? Not all quarantines are alike; each carries its own risks and benefits.

If this were idle presidential speculation, it wouldn't be worrisome. But he isn't the only one talking about quarantines and calling in the troops. In an Oct. 5 interview on "The NewsHour With Jim Lehrer," Julie Gerberding, director of the Centers for Disease Control and Prevention, also wondered whether the government would need to turn to "containment" or "quarantine the people who are exposed." She too remarked that the military or the National Guard might be summoned "to maintain civil order, in the context of scarce resources or an overwhelming epidemic. . . . It would be foolish not to at least consider it and plan for that as a possibility."

This is an example of a cure that is as frightening as the disease. It is hard to imagine how the military would oversee a quarantined area. If a health worker, drug addict or teenager attempted to break the quarantine, what would soldiers do? Shoot on sight? Teenagers and health workers were the people who most often violated quarantine rules in Toronto during the severe acute respiratory syndrome (SARS) scare in 2003. Moreover, the use of a quarantine to control a flu pandemic isn't only a potential threat to life and civil liberties; it's also a waste of money, resources and time. The reason: There isn't any kind of quarantine that will do any good -- at least not for a pandemic influenza.

Quarantine, from the Italian "quarantina," which means "space of 40 days," dates from 15th-century regulations devised in certain Italian cities to control the spread of plague by sequestering those thought to have been exposed to the disease. Along with isolation -- secluding those who are clearly sick -- it can be an effective tool for controlling outbreaks of certain types of disease. In 1910 and 1920, before antibiotics, plague experts in Manchuria controlled several deadly outbreaks of pneumonic plague using quarantine and isolation alone. But pneumonic plague, now rare, spreads in a very different way than flu does. Pneumonic plague germs are coughed out in large droplets that quickly fall to the ground. If you are more than six feet away from a plague patient, you're unlikely to catch the disease. Also, plague patients are typically very ill before they can transmit the germ to others. "There is no disease more susceptible to quarantine than plague," wrote the physician Wu Lien-teh, who helped break the Manchurian epidemics.

Influenza is entirely different. The virus spreads explosively. Coughing, sneezing, or even speaking launches flu particles in an aerosol cloud of tiny droplets, which can drift in the air for some distance. Physician and flu researcher Edwin Kilbourne, who worked with flu patients during the pandemic of 1957-58, points out that people with flu may shed the virus even before they know they're sick -- not much, but enough to transmit the disease. Worse, some 10 to 20 percent of flu patients have subclinical infections; they never look sick at all. Yet they can still spread infection. Faced with a flu pandemic, you'd hardly know where the disease was coming from.

How can you quarantine a disease like that? According to Kilbourne, you can't. "I think it is totally unreasonable on the basis of every pandemic we've had," says Kilbourne. "Every earlier pandemic seeded in multiple foci at the same time. Quarantine simply will not work."

Indeed, a strictly enforced quarantine could do more harm than good. Herding large numbers of possibly infected people together makes it likely that any influenza strain passed among them would actually increase in virulence. Usually, in order to spread, human flu germs need hosts mobile enough to walk around and sneeze on other people. Those flu strains so deadly that they kill or disable their hosts won't get the chance to spread and will die off. This keeps human flu virulence within bounds.

The signal exception is the 1918 flu, which acquired its extreme lethality, according to University of Louisville evolutionary biologist Paul W. Ewald, in the crowded and terrible conditions on the Western Front during World War I. Troops by the train and truckload were constantly being moved in and out of this petri dish, meaning a severely flu-stricken soldier didn't have to move much to infect others.

Suppose that a government official today decided to round up exposed people and move them to a space like the Superdome in New Orleans. It's unlikely that even a crowded Superdome could replicate the conditions on the Western Front. But, depending on how densely packed people were, you could expect the flu strain trapped among them to increase in virulence. You'd be breeding a deadlier flu.

If you let people walk around freely, only those strains mild enough to allow people to stay on their feet would spread easily.

If quarantine won't work, what would? What about medication? Kilbourne is not optimistic about the vaunted (and expensive) antiviral drug Tamiflu, which can be taken to prevent or treat flu. "The problem with antivirals is that they are untried on any mass basis," says Kilbourne. "How long are you going to keep people on antivirals? Also, we don't know about any side effects of the newer antivirals. Older antivirals cause neurological problems in older people."

Kilbourne thinks that preventive vaccines are our best, and only, strategy for combating a pandemic flu threat. The new vaccine, developed with National Institutes of Health sponsorship, shows some ability to protect. But Kilbourne, who in 1969 developed the first reassortant flu vaccine (one made by combining snippets of genetic material from different flu strains), isn't enthusiastic. First, the new vaccine must be given in two doses, at very high concentrations. And it's hard to grow. Kilbourne adds, "We don't have enough if a pandemic happened tomorrow."

Still, vaccination is the gold standard for pandemic preparation -- once we know that a contagious human disease is emerging and the risk of vaccination becomes less than the risk of disease.

That's a long way from now. Despite all the hysteria, there isn't a shred of evidence that a pandemic is actually on the way. Developing new flu vaccines is a useful thing to do. Pandemic or not, flu kills thousands every year. But devising quarantine plans is useless.